The present invention relates to an autonomous mowing vehicle and an apparatus for detecting a boundary between a field which already has been mowed by the autonomous mowing vehicle and a field which has not been mowed yet.
Japanese laid-open patent application No. 1-312610 proposes a system for detecting a self-position of an autonomous mowing vehicle, using a magnetic sensor which detects the magnetic field generated by a cable buried under the ground. However, it is difficult to bury cables throughout a large area, such as a golf course, riverbed or park, for the autonomous running of an unmanned mowing vehicle. Even if it is possible to do this, the cost runs up.
To resolve this problem, several systems which detect a boundary between a mowed field and an unmowed field to be followed by the autonomous mowing vehicle, have been developed.
As a first example of such systems, Japanese laid-open patent application No. 61-139304 introduces a system which detects a boundary between mowed and not mowed fields to be followed by an autonomous mowing vehicle by binarizing an image picture including the boundary sensed by a camera with respect to averaged lightness and analyzing the binarized image picture.
However, this system must be expensive because of the provision of a camera and image processing unit. Furthermore, cleaning and maintenance of the camera is frequently needed because splashed mud or dust adhering on a camera lens prevents taking clear images. It is also inconvenient that the camera is not resistant to against water.
Japanese published patent application No. 4-39286 introduces a second example including a plurality of optical sensors, as the type of photointerrupter, secured to a front frame and a rear frame of a mowing vehicle, aligning in a lateral direction thereof. Each sensor is composed of a light emitting element and a light receiving element facing each other through a slit in the lateral direction of the mowing vehicle to detect the presence or absence of the lawn grass therebetween. The system determines that the mowing vehicle is surely following a boundary between mowed and not mowed fields when, simultaneously, one of the optical sensor detects the presence of the lawn grass and another one of the sensor detects the absence of the lawn grass.
In this second example, however, splashed mud or dust adhering on a surface of at least one of the light emitting element and the light receiving element may affect the passage of light therebetween, which causes erroneous determinations that the lawn grass is present even if it is actually absent. Furthermore, such optical sensors rigidly secured on the frames of the mowing vehicle are required to be positioned at a particular height from the ground to prevent the sensors from being damaged by hitting the ground. However, if the sensors are so positioned, it is impossible to detect the boundary in the case where height of the lawn grass to be mowed is relatively short, for instance, in the case of mowing the green of the golf course.